1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus discharging staying toner.
2. Description of the Related Art
Electrophotographic image forming apparatus (such as multi-function peripherals (MFPs), facsimile devices, copiers and printers) incorporate a developing device for performing development using toner.
Document 1, specified below, discloses an image forming apparatus that counts the number of rotations of the developer roller and the number of dots in images created on the photoreceptor drum in order to minimize the decrease of image quality due to deterioration of toner. It performs a development process using a developer (i.e. it discharges staying toner) if the number of dots in the images for a prescribed number of rotations of the developer roller is smaller than a predetermined threshold.    [Document 1] JP 2004-125829 A
Image forming apparatus that discharge the staying toner when the staying toner exceeds a predetermined amount may consume toner unnecessarily. It can be explained as follows:
If the dot count for the image that will be printed immediately after the staying toner exceeds a predetermined amount is relatively high (i.e. the image consumes a relatively large amount of toner), printing that image may result in an amount of staying toner smaller than the predetermined value. Even when this is the case, a conventional image forming apparatus discharges the staying toner when the staying toner exceeds the predetermined amount, which means that it may discharge staying toner that does not have to be discharged.
Further, an image forming apparatus performs image stabilization in order to keep producing proper images. It uses the developing device to print a pattern, which is then detected and used for positioning of images and for density control.
Performing image stabilization results in an increased amount of staying toner. If the staying toner is discharged each time an image stabilization process is performed following a power-on, toner is consumed even when no printing is performed.
Image stabilization may be performed while printing is interrupted, and an image with a relatively large toner consumption may be printed directly after the interruption, in which case the staying toner would not have to be discharged after the image stabilization.